import java.util.Scanner;

public class c1 {
    //定义三个无参数无返回值方法，分别实现计算三角形、正方形、长方形的面积。
    public static void main(String[] args) {
        chanfgangxing();
    }

    public static void chanfgangxing() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("长方形的长：");
        double h = scanner.nextDouble();
        System.out.println("长方形的宽：");
        double a = scanner.nextDouble();
        double S = a * h;
        System.out.println(S);
    }
    public static void zhengfangxing() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("正方形的边长：");
        double h = scanner.nextDouble();
        double S = h * h;
        System.out.println(S);
    }
    public static void sanjiapxing() {
        Scanner scanner = new Scanner(System.in);
        System.out.println("三角形的高：");
        double h = scanner.nextDouble();
        System.out.println("三角形的底：");
        double a = scanner.nextDouble();
        double S = 1 / 2 * a * h;
        System.out.println(S);

    }
}
